[llvm] [llvm][CodeGen] Fix the empty interval issue in Window Scheduler(#128714) (PR #129204)

[Hua Tian via llvm-commits]

huaatian wrote:

A virtual register's ​LiveInterval​ is empty in ​updatePressureDiff()​. This virtual register was generated by the ​ModuloScheduleExpander​ after a successful modulo scheduling in the previous step.
Therefore, the root cause of this issue is that: the newly generated MIs by the ​ModuloScheduleExpander​ do not properly maintain the ​LiveInterval​ information.
![image](https://github.com/user-attachments/assets/a6591ad4-db20-4d7b-b24e-4ca343af38f6)
![image](https://github.com/user-attachments/assets/72ae4200-8b3e-4882-9231-d55cb5316833)
![image](https://github.com/user-attachments/assets/3e31c443-27ae-4fbb-a6cf-5bf163cca087)



https://github.com/llvm/llvm-project/pull/129204